Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$29.69	12.294%	$33.3401	$33.34	$33.35	$33.30
Purchase #2	$166.82	12.207%	$187.1837	$187.18	$187.20	$187.20
Purchase #3	$92.97	10.585%	$102.8109	$102.81	$102.80	$102.80
Purchase #4	$80.70	3.339%	$83.3946	$83.39	$83.40	$83.40
Purchase #5	$87.60	13.103%	$99.0782	$99.08	$99.10	$99.10
Purchase #6	$36.34	3.421%	$37.5832	$37.58	$37.60	$37.60
Purchase #7	$156.50	6.464%	$166.6162	$166.62	$166.60	$166.60
7 purchase totals =	$650.62		$710.0069	$710.00	$710.05	$710.00